Historically, many operating conditions provide unfavorable braking situations. When an assist device, such as a dynamic retarder or energy storage device is utilized, the device can change the vehicle brake proportioning resulting in braking variations if the assist is rapidly reduced or fully satisfied. This variation in braking torque can result in the operator sensing necessity for more braking effort thereby applying more energy to the brake pedal. This can cause stoppage of the vehicle more rapidly than the driver had intended.
In regenerative energy recovery systems in an electric or hybrid powertrain, the driver feel of the braking system can be affected by the storage device energy level. That is, the charge of the storage battery's electrical system or perhaps the energy in the flywheel or an accumulator and other systems. Weather conditions and system thermal conditions can also affect the braking feel of the driver.
Since the regeneration of energy is applied to one axle in a power system, the brake balance between a front axle and a rear axle can be affected. If the regeneration recovery system has a discontinuing condition, the resultant difference in brake torque at the axle can be perceived by operator as a loss in braking effort although the brake system is functioning quite well. The regeneration storage systems are an assist mechanism to improve fuel economy by recovering the maximum available potential and kinetic energies.
To make maximum use of such systems, the driver must be provided with a system in which the regenerative storage braking mechanism is transparent during all operating conditions of the vehicle that might occur.